ME3162/ME3162E
NATIONAL UNIVERSITY OF SINGAPORE
ME3162/ME3162E – MANUFACTURING PROCESSES (Semester I : AY2012/2013) Time Allowed : 2 Hours
INSTRUCTIONS TO CANDIDATES:
1.
This examination paper contains SEVEN (7) questions and comprises TEN (10) printed pages.
2.
Answer ALL questions.
3.
This is an OPEN-BOOK EXAMINATION.
PAGE 2
QUESTION 1
Figure 1
ME3162/ME3162E
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ME3162/ME3162E
Figure 1 above shows a table laid out for a birthday party. Below is a list of ten of the items:
Serial number
Material
a
Polyethylene fruit juice bottle
b
Stainless steel stew pot
c
Polystyrene forks and spoons
d
Steel knife
e
Melamine plate
f
Polypropylene drinking straw
g
Stainless steel cup
h
Styrofoam cup
i
PVC sheet covering table top
j
Round hollow mild steel leg
Manufacturing process
Match the following ten manufacturing processes to the ten cases above. For your answer, simply reproduce the table above and fill in the correct capital alphabets in the right-hand column. Explanations and words are not necessary. A. B. C. D. E. F. G. H. I. J.
Stamping from sheet and pressing to shape Extrusion Deep drawing Injection molding Compression molding Calendaring Blow molding Rolling and welding seam Forging Foam molding (20 marks)
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ME3162/ME3162E
QUESTION 2
Figure 2
(a)
The compression springs in Figure 2 are 120 mm high and made of aluminium. The coil internal diameter is 40 mm and the wire is 5 mm in diameter. Which one of the four methods of production do you think is the correct one? (i)
Hot extrude the aluminium bar, hot tensile draw to 5 mm mandrel of diameter 40 mm. (ii) Cold extrude the aluminium bar, cold tensile draw to 5 mm mandrel of diameter 40 mm. (iii) Hot extrude the aluminium bar, cold tensile draw to 5 mm mandrel of diameter 40 mm. (iv) Cold extrude the aluminium bar, hot tensile draw to 5 mm mandrel of diameter 40 mm.
diameter, coil on diameter, coil on diameter, coil on diameter, coil on (4 marks)
(b)
Which one of the four methods is the correct one for producing a cold-rolled mild steel sheet of 1 mm thickness? (i)
Cold roll a 30 cm by 30 cm mild steel billet through a series of rollers to 1 mm thickness. (ii) Hot extrude a 30 cm by 30 cm mild steel billet down to 5 mm thickness, pickle in acid, cold roll through a series of rollers to 1 mm thickness. (iii) Hot extrude a 30 cm by 30 cm mild steel billet down to 5 mm thickness, pickle in acid, cold tensile draw through a series of dies to 1 mm thickness (iv) Hot roll a 30 cm by 30 cm mild steel billet down to 3 mm thickness through a series of rollers, pickle in acid, cold roll through a series of rollers to 1 mm thickness. (4 marks)
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ME3162/ME3162E
QUESTION 3 (a)
The wok (frying pan) shown in Figure 3 is made of stainless steel. Which of the following methods of manufacture is most suitable for mass production?
Figure 3
(i)
Punch a circular blank from stainless steel sheet, cold draw into the wok shape, join the handles to the wok by rivets (ii) Punch a circular blank from stainless steel sheet, cold draw into the wok shape, join the handles to the wok by resistance spot welding (iii) Punch a circular blank from stainless steel sheet, hot draw into the wok shape, join the handles to the wok by rivets (iv) Punch a circular blank from stainless steel sheet, hot draw into the wok shape, join the handles to the wok by resistance spot welding (3 marks) (b)
If the pan were made of aluminium, which of the following methods of manufacture is most suitable for mass production? (i)
Punch a circular blank from aluminium sheet, cold draw into the wok shape, join the handles to wok by rivets (ii) Punch a circular blank from aluminium sheet, cold draw into the wok shape, join the handles to wok by resistance spot welding (iii) Punch a circular blank from aluminium sheet, hot draw into the wok shape, join the handles to wok by rivets (iv) Punch a circular blank from aluminium sheet, hot draw into the wok shape, join the handles to wok by resistance spot welding
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ME3162/ME3162E
(3 marks) (c)
In ancient times, the wok in Figure 4 could only be manufactured using cast iron by sand casting and not by the above methods. Which one of the following is the WRONG reason why?
Figure 4
(i) (ii) (iii) (iv)
They were not able to extract aluminium from the ore They were not able to produce stainless steel They did not have rolling mills to produce sheet metal They wanted to manufacture the wok in one single piece (3 marks)
(d)
In modern times, why is sand casting never used to produce stainless steel or aluminium woks? (i) (ii) (iii) (iv)
The product will be too brittle It is too slow a production method for these materials It is not possible to sand cast stainless steel or aluminium into that shape The product will lose corrosion resistance (3 marks)
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ME3162/ME3162E
QUESTION 4
Figure 5
(a)
Figure 5 above shows an ornamental (decorative) “money tree” made of Royal Selangor Pewter. Pewter is an alloy containing mainly tin, with small percentages of other metals. The melting point of the pewter alloy is below 200 C. The tree is 15 cm high. Which one of the four answers below lists the correct possible methods for producing a batch of 500 pieces? (i) (ii) (iii) (iv)
Investment casting, die casting and forging from sheet Forging from sheet, powder metallurgy and sand casting Die casting, investment casting and sand casting Sand casting, powder metallurgy and investment casting (5 marks)
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(b)
ME3162/ME3162E
How would you manufacture a few special “money trees” of this shape which are reduced in size to just 1 cm high and without the holes in the middle of the coins? (3 marks)
QUESTION 5 (a)
The following are four possible secondary operations that can be performed on a steel part produced by powder metallurgy, some with and some without any effect on the original strength of the product. Reproduce the table below and put a tick in the appropriate box.
Operation
Strength increased
Strength decreased
Strength unchanged
Impregnate the pores with oil Infiltrate the pores with copper Machine screw threads Press forge to improve dimensional tolerance (4 marks)
Figure 6
(b)
Your company received three samples (Figure 6 a, b and c) of a go-kart steering wheel made of low carbon steel but manufactured by three different methods. The supplier told you that one was blanked and pierced from a 2 mm cold rolled sheet, one was hot press forged, and one was die cast. Unfortunately they have been careless and lost the labels, so they no longer know which is which. Laboratory tests were used to reveal their microstructures (as shown in the Figure). Your boss wants you to clear the mix-up, knowing you scored A+ for the NUS Manufacturing Process exam. Give an educated guess as to which method of production was used for each specimen. (Explanations are not necessary.) (6 marks)
(c)
Give reasons why it would be better to make the steering wheel out of a plastic like ABS (acrylonitrile butadiene styrene) for a child’s go-kart. Brief answers in point form will suffice. (7 marks)
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ME3162/ME3162E
QUESTION 6 A 170 mm diameter steel shaft is to be machined by turning process. The length of the shaft should be 260 mm. The machine has a 10 KW motor which offers maximum 75 percent efficiency. The bar stock has a diameter of 180 mm and length of 300 mm. The specific cutting energy, ps, for steel is 2.73 GJ/m3. Loading and unloading time for the workpiece is 2 minutes. Machining time for both roughing and finishing should not exceed 12 minutes. Select the cutting speed, feed and depth of cut for both roughing and finishing operations. (21 marks)
QUESTION 7 (a)
If the workpiece material is steel what will be the appropriate cutting speed for tungsten carbide tool? (i) (ii) (iii) (iv)
20 m/min 40 m/min 100 m/min 300 m/min (2 marks)
(b)
If the workpiece material is steel which of the following tool materials should not be used? (i) (ii) (iii) (iv)
Ceramic Tungsten carbide High speed steel Diamond (2 marks)
(c)
If a diamond tool is used for machining a aluminium workpiece material what will be the appropriate cutting speed? (i) (ii) (iii) (iv)
80 m/min 100 m/min 200 m/min 500 m/min (2 marks)
(d)
If a High Speed Steel tool is used for machining a steel workpiece material what will be the appropriate cutting speed? (i) (ii) (iii) (iv)
200 m/min 150 m/min 40 m/min 300 m/min (2 marks)
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(e)
ME3162/ME3162E
Which of the following rake angles will give the best surface finish? (i) – 15 degrees (ii) – 5 degrees (iii) 0 degree (iv) +10 degrees (2 marks)
(f)
Which statement is correct? (i) (ii) (iii) (iv)
Higher the cobalt content, harder will be the tool Lower the cobalt content, harder will be the tool Cobalt content has no effect on the hardness of the tool None of the above (2 marks)
(g)
Which statement is correct? (i) (ii) (iii) (iv)
Specific cutting energy increases with the increase of the edge radius of the tool Specific cutting energy decreases with the increase of the edge radius of the tool Specific cutting energy increases with the increase of cutting speed. Edge radius of the tool has no effect on specific cutting energy (2 marks)
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